The disclosure of Japanese Patent Application No. 2001-320233 filed on Oct. 18, 2001 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates generally to a cylindrical vibration damping device including: an inner shaft member; an outer sleeve member disposed radially outward of the inner shaft member; and a rubber elastic body elastically connecting the inner shaft member and the outer sleeve member. More particularly, the present invention is concerned with a fluid-filled cylindrical vibration damping device capable of exhibiting a vibration damping or isolating effect based on flows or resonance of a fluid contained therein, and being suitably employed as an engine mount, a body mount a differential mount, a suspension bushing or other mounts for use in automotive vehicles, for example.
2. Description of the Related Art
A fluid-filled cylindrical vibration damping device is known as one type of a vibration damping mount or bushing interposed between two members of a vibration system for elastically connecting two members or for elastically mounting on one of the two members on the other in a vibration damping or isolating fashion. A known example of the fluid-filled cylindrical vibration damping device is disclosed in JP-B-63-3763 or JP-B-5-55739, which includes an inner shaft member attachable to one of the two members of the vibration system, an outer sleeve member attachable to the other member of the vibration system and disposed radially outwardly of the inner shaft member with a radial spacing therebetween, and a rubber elastic body interposed between the inner shaft member and the outer sleeve member for elastically connecting these two members and defining a plurality of fluid chambers between these two members. These fluid chambers are filled with a non-compressible fluid, and are held in fluid communication with each other through at least one orifice passage. An application of a vibrational load to the fluid-filed vibration damping device constructed as described above induces fluid pressure variation between these fluid chambers, thereby causing flows of the fluid through the orifice passage. Thus, the fluid-filled vibration damping device is able to exhibit an excellent vibration damping effect based on flows or resonance of the fluid flowing through the orifice passage, which effect is never achieved by an elastic mount whose damping effects are only based on the rubber elastic body. For this advantage, the conventional fluid-filled cylindrical vibration damping device is preferably employed as an engine mount for use in an automotive vehicle.
However, the above-described conventional fluid-filled cylindrical vibration damping device exhibits an effective vibration damping or isolating effect based on the fluid flows through the orifice passage, with respect to only input vibrations in a relatively narrow frequency range to which the orifice passage is tuned. In particular, the conventional vibration damping device experiences considerable deterioration in its damping capability when the input vibration has a frequency higher than the frequency to which the orifice passage is tuned.
For the above-described inherent problem, the conventional fluid-filled cylindrical vibration damping device, when being used as an engine mount for an automotive vehicle with its orifice passage is tuned to a frequency range corresponding to engine shakes required to be damped upon driving of the vehicle, or corresponding to engine idling vibrations required to be damped upon idling of the vehicle, is not able to exhibit a desired high damping effect upon application of the engine shakes or a desired vibration isolating effect upon application of the engine idling vibrations for a wide frequency range enough to meet requirements. In particular, the damping capability of the conventional vibration damping device is considerably deteriorated immediately after the input vibration has a frequency higher than the frequency to which the orifice passage is tuned.
Meanwhile, JP-A-9-21441 and JP-A-8-14311 disclose another example of the vibration damping device suitably usable as an engine mount for an automotive vehicle, other than the fluid-filled cylindrical vibration damping device directed to the present invention. The disclosed vibration damping device includes a block-shaped first mounting member, a large-diameter cup-shaped second mounting member and a rubber elastic body interposed between the second mounting member and the first mounting member disposed on the side of an open end portion of the second mounting member for elastically connecting the first and the second mounting members with each other and fluid-tightly closing the open end of the second mounting member, thereby defining a fluid chamber filled with a non-compressible fluid. The disclosed non-cylindrical type fluid-filled vibration damping device has a relatively large inner space in comparison with the fluid-filled cylindrical vibration damping device. For this advantage, the non-cylindrical type fluid-filled vibration damping device, as disclosed in the above-mentioned publications, is able to incorporate therein a switch valve for alternately effecting a plurality of orifice passages tuned to different frequency ranges, or a fluid-pressure absorbing mechanism having a movable plate for limiting an amount of flows of the fluid. This arrangement makes it possible for the non-cylindrical type fluid-filled vibration damping device to easily exhibit a desired vibration damping or isolating effect based on resonance or flows of the fluid through the orifice passage over an expanded or a wide frequency range of vibrations. However, the present invention is directed to the fluid-filled cylindrical vibration damping device wherein the inner shaft member is disposed in the central portion of the bore of the outer sleeve member with a substantially coaxial relationship with each other, making it significantly difficult to incorporate such a complicated mechanism of the orifice passages and the switch valve or such a fluid-pressure absorbing mechanism into the bore of the outer sleeve member of the fluid-filled cylindrical vibration damping device. Further, the use of these mechanisms causes considerable deterioration in efficiency and economy of manufacture of the fluid-filled cylindrical vibration damping device, thus being ineffective to improve the damping capability of the fluid-filled cylindrical vibration damping device.
It is therefore one object of this invention to provide a fluid-filled cylindrical vibration damping device novel in construction and capable of exhibiting an excellent vibration damping and/or isolating effect based on resonance or flows of the fluid through an orifice passage or passages with respect to vibrations over an expanded or wide frequency range, with simple structure.
The above and/or optional objects of this invention may be attained according to at least one of the following modes of the invention. Each of these modes of the invention is numbered like the appended claims and depending from the other mode or modes, where appropriate, to indicate possible combinations of elements or technical features of the invention. It is to be understood that the principle of the invention is not limited to these modes of the invention and combinations of the technical features, but may otherwise be recognized based on the teachings of the present invention disclosed in the entire specification and drawings or that may be recognized by those skilled in the art in the light of the present disclosure in its entirety.
(1) A fluid-filled cylindrical vibration damping device including: (a) an inner shaft member; (b) an outer sleeve member disposed radially outwardly of the inner shaft member in a spaced-apart relationship with the inner shaft member; (c) an elastic body interposed between the inner shaft member and the outer sleeve member for elastically connecting the inner shaft member and the outer sleeve member with each other; (d) a plurality of fluid chambers formed between the inner shaft member and the outer sleeve member and filled with a non-compressible fluid so that fluid pressures in the plurality of fluid chambers vary relative to each other upon application of a vibrational load to the vibration damping device; and (e) a first orifice passage permitting a fluid communication between the plurality of fluid chambers and being at least partially defined by an elastic member adapted to be subjected to shear deformation as a result of increase of a fluid pressure acting on the first orifice passage so that a cross sectional area of the first orifice passage increases according to an increase of the fluid pressure acting on the first orifice passage owing to the shear deformation of the elastic member.
In the fluid-filled cylindrical vibration damping device constructed according to this mode of the invention, if a frequency of an input vibration exceeds an initial or static tuning frequency of the first orifice passage (i.e., a frequency range to which the first orifice passage is tuned in a condition where the elastic member is not subjected to shear deformation), a resistance to flows of the fluid through the first orifice passage is considerably increased, and the fluid pressure acting on the first orifice passage is accordingly increased. The elastic member at least partially defining the first orifice passage is elastically deformed due to the increased fluid pressure acting thereon, so as to gradually increase the cross sectional area of the first orifice passage with the increase of the fluid pressure acting on the first orifice passage. This makes it possible to shift the tuning frequency of the first orifice passage to a higher frequency range. That is, the first orifice passage of the fluid-filled cylindrical vibration damping device of this mode of the invention is capable of changing its tuning frequency from the above-indicated initial tuning frequency to a higher frequency range, as if it follows the change of frequencies of input vibrations. If the input vibration has a frequency higher than the initial tuning frequency of the first orifice passage, for example, the tuning frequency of the first orifice passage increases with an increase of the frequency of the input vibration, permitting the fluid-filled cylindrical vibration damping device of this mode of the invention to exhibit an excellent vibration damping effect based on the resonance or flows of the fluid through the first orifice passage, with respect to the input vibrations over a higher frequency range. Thus, the fluid-filled cylindrical vibration damping device of this mode of the invention is capable of exhibiting a desired damping effect based on the resonance or flows of the fluid through the first orifice passage with respect to input vibrations over a wide frequency range, while eliminating the conventionally experienced problem of the considerable deterioration of its vibration damping or isolating capability upon application of the vibrational load whose frequency is higher than the initial tuning frequency of the first orifice passage.
In particular, the first orifice passage is always held in fluid communication with the fluid chambers, and is partially defined by the elastic member that is elastically deformable due to the fluid pressure acting on the first orifice passage. This arrangement permits a gradual and considerable increase of an amount of elastic deformation of the elastic member and a resultant gradual and considerable increase of the cross sectional area of the first orifice passage, according to the increase of the fluid pressure acting on the first orifice passage. This eliminates a problem of abrupt elastic deformation of the elastic member which may occur when the first orifice passage partially defined by a check-like elastic member operable for open-ably checking the first orifice member, and when the pressure of the fluid acting on the first orifice passage reaches a limit value for opening the check-like elastic member, for example. Therefore, when the frequency of the input vibration shifts to a higher frequency range, the fluid-filled cylindrical vibration damping device is able to change the tuning frequency of the first orifice passage so as to substantially correspond to the level of the frequency of the input vibration, thus permitting the fluid-filled cylindrical vibration damping device of this mode of the invention to exhibit an excellent vibration damping or isolating capability over a wide frequency range of the input vibrations.
Since the elastic member at least partially defining the first orifice passage is arranged to be elastically deformed with shear deformation when the fluid pressure acting on the first orifice passage increases, the elastic member can be elastically deformed with high sensitivity with respect to the increase of the fluid pressure acting on the first orifice passage, and with a larger amount of deformation with respect to a given amount of the increase of the fluid pressure acting on the first orifice passage, in comparison with the case where the elastic member is elastically deformed with compression deformation as a primary component. This arrangement allows the first orifice passage to change its tuning frequency so as to follow the change of frequencies of the input vibrations over a sufficiently wide frequency range, with high accuracy. Thus, the fluid-filled cylindrical vibration damping device according to this mode of the invention is capable of exhibiting an excellent vibration damping or isolating capability over the sufficiently wide frequency range of the input vibrations.
(2) A fluid-filled cylindrical vibration damping device according to the above-indicated mode (1), wherein the elastic member comprises an elastic protruding portion, which protrudes into an interior area of the first orifice passage so as to partially narrow the first orifice passage. According to this mode of the invention, the elastic member is formed by the elastic protruding portion whose dimension is made smaller than the entire length of the first orifice passage, making it possible to elastically deform the elastic member with a relatively small fluid pressure acting thereon and with stability. Therefore, the first orifice passage of the fluid-filled cylindrical vibration damping device of this mode of the invention is capable of changing its tuning frequency so as to follow the change of the fluid pressure acting on the first orifice passage caused by the change of the input vibration frequencies, with high sensitivity and accuracy.
(3) A fluid-filled cylindrical vibration damping device according to the above-indicated mode (2), wherein the elastic protruding portion protrudes into the interior area of the first orifice passage with a width dimension over an entire width of the first orifice passage, and includes a narrow groove formed at an intermediate portion in a widthwise direction of a protruding end portion thereof so as to extend in a longitudinal direction of the first orifice passage, the elastic protruding portion being held at a protruding end surface of the protruding end portion thereof at opposite sides of the narrow groove in the widthwise direction with an inner surface of the first orifice passage. In this arrangement, the first orifice passage is narrowed at a portion thereof over the entire width thereof by the elastic protruding portion, so that the fluid pressure can effectively act on the elastic protruding portion. Also, the elastic protruding portion is held in contact at its protruding end portion with the inner surface of the first orifice passage. Therefore, the shapes or states of the narrow groove and the first orifice passage are held in their initial state with high stability, until the fluid pressure applied to the first orifice passage reaches a given limit value, thus making it possible to stabilize an initial vibration damping or isolating capability of the fluid-filled cylindrical vibration damping device based on flows of the fluid through the first orifice passage.
(4) A fluid-filled cylindrical vibration damping device according to the above-indicated mode (2) or (3), wherein the elastic protruding portion is inclined to one of opposite sides in the longitudinal direction of the first orifice passage so that the elastic protruding portion exhibits a soft spring characteristic with respect to the fluid pressure applied thereto from an other one of opposite sides in the longitudinal direction of the first orifice passage. According to this mode of the invention, a void is formed between the elastic protruding portion and the inner wall of the first orifice passage on the one side of the first orifice passage to which the elastic protruding portion is inclined. This allows the elastic protruding portion to be effectively deformed in the direction in which the cross sectional area of the first orifice passage increases, when the fluid pressure applied to the first orifice passage acts on the elastic protruding portion. Since the elastic protruding portion can be elastically deformed with high sensitivity in response to the fluid pressure acting on the first orifice passage, the tuning frequency of the first orifice passage can be changed with high accuracy in response to the frequency of the input vibration. Thus, the fluid-filled cylindrical vibration damping device can exhibit a high vibration damping effect with respect to the input vibrations over a wide frequency range.
(5) A fluid-filled cylindrical vibration damping device according to the above-indicated mode (4), wherein the vibration damping device includes a plurality of the first orifice passages that are arranged in parallel to each other and are respectively provided with the elastic protruding portions inclined to respective directions different from each other. According to this mode of the invention, the plurality of the first orifice passages cooperate to each other to compensate a problem of directions in the elastic deformation of the elastic protruding portions thereof. Namely, this arrangement allows the fluid-filled cylindrical vibration damping device to change the tuning frequency of any one of the first orifice passages thereof and characteristics of a resultant flows of the fluid between the fluid chambers, so as to follow the change of the frequencies of the input vibrations in any directions. Thus, the fluid-filled cylindrical vibration damping device is capable of exhibiting a further improved vibration damping or isolating effect at a desired higher frequency range of the input vibrations.
(6) A fluid-filled cylindrical vibration damping device according to the above-indicated mode (4) or (5), wherein the elastic body includes a groove open in an outer circumferential surface thereof, whose opening is fluid-tightly closed by the outer sleeve member to thereby form the first orifice passage, and the elastic protruding portion is integrally formed with the elastic body such that the elastic protruding portion is formed at at least one of opposite open-end portions of the first orifice passage so as to protrude radially outwardly from a bottom of the groove while being inclined toward an outward of the one of opposite open-end portions of the first orifice passage. This arrangement makes it possible to form the first orifice passage provided with the elastic protruding portion integrally formed with the elastic body with simplicity and ease. In particular, since the elastic protruding portion is formed at at least one of opposite open-end portions of the first orifice passage, the elastic protruding portion can be designed in terms of its inclined angle or the like, with high degree of freedom, and can be formed so as to permit a large amount of elastic deformation thereof.
(7) A fluid-filled cylindrical vibration damping device according to any one of the above-indicated modes (4)-(6), wherein the elastic body includes a groove open in an outer circumferential surface thereof, whose opening is fluid-tightly closed by the outer sleeve member to thereby form the first orifice passage, and the elastic protruding portion is integrally formed with the elastic body such that the elastic protruding portion is formed at a longitudinally intermediate portion of the groove so as to protrude radially outwardly from a bottom of the groove while extending toward one of longitudinally opposite sides of the groove inside the groove. This arrangement makes it possible to form the first orifice passage provided with the elastic protruding portion with simplicity and ease. Also, the elastic protruding portion can be designed in terms of its longitudinal length with high degree of freedom. The first orifice passage should be provided with at least one elastic protruding portion. A plurality of the elastic protruding portions may possible be formed in the first orifice passage, while being independent of each other in the longitudinal direction, depending upon required vibration damping characteristics of the fluid-filled cylindrical vibration damping device. With the help of the provision of the plurality of the elastic protruding portions, the first orifice passage can have a narrowed portion with a relatively large length, while ensuring low spring characteristics of the elastic protruding portions.
(8) A fluid-filled cylindrical vibration damping device according to the above-indicated mode (6) or (7), further comprising an intermediate sleeve member disposed radially outwardly of the inner shaft member in a spaced-apart relationship with the inner shaft member, and elastically connected with the inner shaft member via the elastic body interposed therebetween upon vulcanization of a rubber material for forming the elastic body, while the outer sleeve member is press-fitted onto the intermediate sleeve member, the groove being open in an outer circumferential surface of the intermediate sleeve member. According to this mode of the invention, the first orifice passage is defined by and between the intermediate and the outer sleeve members formed of a metal or other rigid materials, thus ensuring a high dimensional accuracy and shape stability of the first orifice passage. Preferably, a sealing rubber layer may be bonded to the outer circumferential surface of the intermediate sleeve member upon vulcanizing a rubber material, for assuring a fluid-tight sealing between the intermediate and outer sleeve members. More preferably, the sealing rubber layer may be utilized to form the groove open in the outer circumferential surface of the intermediate sleeve member, making it possible to easily form and design the groove with a high degree of freedom. In this case, the sealing rubber layer defining the groove, and the elastic protruding portion are integrally formed with each other, preferably. Yet more preferably, the sealing rubber layer may be integrally formed with the elastic body.
(9) A fluid-filled cylindrical vibration damping device according to any one of the above-indicated modes (1)-(8), further comprising a second orifice passage disposed in a parallel relationship with the first orifice passage, wherein the first and second orifice passages are relatively tuned such that the first orifice passage permits resonance of fluid flowing therethrough at a first frequency range lower than a resonance frequency range of fluid flowing through the second orifice passage when the first orifice passage is in a condition where the elastic member is not subjected to shear deformation, and permits resonance of the fluid flowing therethrough at a second frequency range higher than the resonance frequency range of the fluid flowing through the second orifice passage when the first orifice passage is in a condition where the elastic member is subjected to shear deformation. According to this mode of the invention, the fluid-filled cylindrical vibration damping device is able to exhibit a desired vibration damping or isolating effect based on resonance or flows of the fluid through the second orifice passage, when being subjected to vibrations whose frequencies correspond to a predetermined frequency range to which the second orifice passage is fixedly tuned. When the frequency of input vibration is shifted to a higher frequency range, on the other hand, the tuning frequency of the first orifice passage is shifted to the higher frequency range so as to follow the increase of the frequency of the input vibration, thereby preventing the conventionally experienced considerable deterioration of the vibration damping or isolating characteristics of the fluid-filled cylindrical vibration damping device due to an anti-resonance like effect of the fluid flowing through the second orifice passage. Thus, the fluid-filled cylindrical vibration damping device of this mode of the invention is capable of exhibiting a high vibration damping or isolating effect with respect to vibrations over a wide frequency range. In particular, since the second orifice passage is not partially narrowed, unlike the first orifice passage, thus permitting a sufficient amount of fluid to flow through the second orifice passage, resulting in a further improved vibration isolating or damping effect based on the resonance or flows of the fluid through the second orifice passage.
The present invention according to any one of the above-indicated modes (1)-(9) is preferably applicable to a fluid-filled cylindrical vibration damping device wherein the plurality of fluid chambers held in fluid communication with each other through the first orifice passage, comprise a pressure-receiving chamber partially defined by the elastic body and an equilibrium chamber partially defined by a flexible layer. The pressure of the fluid in the pressure-receiving chamber varies due to the elastic deformation of the elastic body upon application of a vibrational load between the inner shaft member and the outer sleeve member, while the volume of the equilibrium chamber is easily variable. The use of the pressure-receiving chamber and the equilibrium chamber is effective to eliminate or absorb an increase of a static pressure of the fluid of these fluid chambers, e.g., when a static load or weight acts on the vibration damping device in its radial direction perpendicular to its axial direction, like an engine mount. Thus, the fluid-filled cylindrical vibration damping device of this mode of the invention can exhibit a desired vibration damping or isolating effect with high stability.
The present invention according to any one of the above-indicated modes (1)-(9) is also preferably applicable to a fluid-filled cylindrical vibration damping device wherein the plurality of the fluid chambers held in fluid communication with each other through the first orifice passage, may comprise a plurality of pressure-receiving chambers, which are partially defined by the elastic body, and are arranged in respective circumferential portions of the elastic body so as to be opposed to each other with the inner shaft member interposed therebetween in a diametric direction in which a vibrational load primarily applied to the vibration damping device. Upon application of the vibrational load to the fluid-filled cylindrical vibration damping device, pressures of the fluids filling these pressure-receiving chambers vary due to the elastic deformation of the elastic body. This type of fluid-filled cylindrical vibration damping device is preferably usable as a suspension bushing or the like wherein no or a relatively small static load is applied to the vibration damping device, and makes it possible to effectively induce fluid pressure variation between the plurality of pressure-receiving chambers connected to each other via the first orifice passage upon application of the vibration to the vibration damping device.